Here's why:
* ASL Sentence Structure: ASL often uses a topic-comment structure. The topic (Alaska trip in November) is established first.
* Negation in ASL: Negation is often conveyed through a combination of sign, facial expression, and a non-manual marker (NMM).
* The NMM: The "non-manual gesture" you mentioned is likely the NMM for negation, which could be a headshake, furrowed brows, or a "tsk" sound.
Therefore, despite saying the trip is still happening, the NMM negates the sentence, meaning he is not going to Alaska in November.